1. Field of the Invention
The present invention relates to a micropump that is a small apparatus for supplying small amounts of a fluid and is used in medical equipment, a chemical analyzer, a microreactor, a biochemical chip or the like, and in particular relates to a check valve device for such a micropump that carries out flow rate control to high accuracy in the case of any of a liquid, a gas or a gas/liquid mixture.
2. Description of the Related Art
Conventionally, as art relating to micropumps that deliver small amounts of liquids, many mechanistic principles have been proposed based on ultra-microfabrication technology called nanotechnology or MEMS (microelectromechanical systems). Such micropumps are used as apparatuses for supplying small amounts of fluids in medical equipment or chemical analyzers, being used for quantitative injection of drugs or for transporting fluids such as mixed reaction gases. The development of small general-purpose micropumps for which highly accurate control is possible is currently still being proceeded with. In general, check valves are often used in micropumps. Under constraints on smallness and thinness, the valve mechanism of such a check valve is required to have springiness (pre-load) so as to make it such that the valve does not open unless the pressure exceeds a certain value. Hereinafter, this springiness is referred to as ‘urging force’.
FIG. 15 is an example of a sectional view showing a conventional micropump. As shown in FIG. 15, such a micropump is often manufactured by laminating together a plurality of plates as described below. FIGS. 16A is a perspective view showing members relating to a check valve device in particular. First, a first valve plate 2, which is a second member, having therein a small-bore inflow hole 2a and a valve mechanism 10B is placed on a first fixing plate 1, which is a first member, having therein a small-bore inflow hole 1a and a large-bore outflow hole 1b for allowing passage of a fluid. A central plate 3, which is a third member, having therein a small-bore inflow hole 3a and a small-bore outflow hole 3b is then placed thereon. A second valve plate 4, which is a fourth member, having therein a valve mechanism 10A and a small-bore outflow hole 4b is then placed on the central plate 3, and a second fixing plate 5, which is a fifth member, having therein a large-bore inflow hole 5a and a small-bore outflow hole 5b is then placed thereon. A diaphragm 7 having a piezoelectric element 8 installed thereon is joined to the second fixing plate 5 via pressure chamber vertical walls 9. The space enclosed by the second fixing plate 5, the pressure chamber vertical walls 9 and the diaphragm 7 shall be referred to as the pressure chamber 6.
Here, the inflow hole 1a in the first fixing plate 1, the inflow hole 2a in the first valve plate 2, the inflow hole 3a in the central plate 3, a large-bore hole 13B provided in the valve mechanism 10A in the second valve plate 4, and the inflow hole 5a in the second fixing plate 5 communicate with one another, thus forming an inflow side flow path through which the fluid is introduced into the pressure chamber 6. Moreover, a pressure chamber 6 communicates with the outflow hole 5b in the second fixing plate 5 and the outflow hole 4b in the second valve plate 4, and the outflow hole 4b in the second valve plate 4 communicates with the outflow hole 3b in the central plate 3, a large-bore hole 13B provided in the valve mechanism 10B in the first valve plate 2, and the outflow hole 1b in the first fixing plate 1, thus forming an outflow side flow path through which the fluid is discharged from the pressure chamber 6. According to this constitution, a micropump having a flow path from the inflow hole 1a of the first fixing plate 1, through the valve mechanism 10A of the second valve plate 4, through the pressure chamber 6, through the valve mechanism 10B of the first valve plate 2, and up to the outflow hole 1b of the first fixing plate 1, and check valve devices due to the valve mechanisms 10A and 10B can be manufactured. Note that the first fixing plate 1 and the second fixing plate 5 have the same shape as one another, but with the face attached to the central plate 3 being reversed. Moreover, as with the fixing plates 1 and 5, the first valve plate 2 and the second valve plate 4 also have the same structure as one another, with only the face attached to the central plate 3 being different.
In the micropump, the valve mechanisms 10A and 10B are disposed in two locations, i.e. in the inflow side flow path and in the outflow side flow path. Here, the valve mechanism in the inflow side flow path is 10A, and the valve mechanism in the outflow side flow path is 10B. The valve mechanisms 10A and 10B are each composed of the large-bore passing hole 13A or 13B which is formed in correspondence to a position and a size of the large-bore hole (the inflow hole 5a or the outflow hole 1b) in the member (the second fixing plate 5 or the first fixing plate 1) on the downstream side of the valve mechanism 10A or 10B relative to the direction of flow of the fluid, a contacting part 11A or 11B for closing the small-bore hole (the inflow hole 3a or the outflow hole 3b) in the central plate 3, the contacting part being formed to face the position of and to have a size corresponding to that of the small-bore hole, and supporting parts 12A or 12B that are formed to bridge across the passing hole 13A or 13B so as to support the contacting part 11A or 11B from both sides. The contacting part 11A or 11B is formed inside this passing hole 13A or 13B to face the position of and to have a size corresponding to the size of the small-bore hole (the inflow hole 3a or the outflow hole 3b) in the central plate 3, which is the member on the upstream side of the valve mechanism 10A or 10B relative to the direction of flow of the fluid. Note that in the following, unless specifically stated otherwise, ‘contacting part 11’ and ‘supporting parts 12’ shall refer to either the contacting part 11A and the supporting parts 12A or the contacting part 11B and the supporting parts 12A. Similarly, ‘valve mechanism 10’ shall refer to either the valve mechanism 10A or the valve mechanism 10B. Moreover, regarding the definition of terminology, the case of a single valve in the valve plate 2 or 4 shall be referred to as ‘valve mechanism’, and the valve mechanism system in which are combined the valve plate 2 or 4 containing the valve mechanism 10, and the first fixing plate 1 and the central plate 3, or the central plate 3 and the second fixing plate 5, that sandwich the valve plate 2 or 4 from either side shall be referred to as ‘check valve device’.
Regarding the urging force of each valve mechanism 10, as with the valve mechanism 10A shown in FIG. 16A, a method using a spacer 15 is usual, but various other inventions have also been disclosed. For example, as shown enlarged in FIG. 16B, there are an invention in which a projecting part 16 is formed from a resin on the contacting part 11B through post-processing (see, for example, Japanese Patent Application Laid-open No. 4-63973 (page 2; page 3, FIG. 1(d))), and an invention in which such a projecting part 16 is formed at the same time as manufacturing the first valve plate 2 having the contacting part 11B therein (see, for example, Japanese Patent Application Laid-open No. 2-308988 (page 2; page 4, FIG. 3)). Furthermore, although not shown in the drawings, there is also an invention in which the contacting part 11 is not planar but rather is formed as a hemispherical projecting part (see, for example, Japanese Patent Application Laid-open No. 2001-12356 (page 2; page 6, FIG. 2)).
Note that as the materials of the members constituting the check valve devices, metallic silicon is often used for each of the valve plates 2 and 4 having supporting parts 12 and a contacting part 11, and glass is often used for the central plate 3 and the fixing plates 1 and 5.
Next, a description of the liquid delivery principle of the micropump and the urging force of each of the check valve devices will be given with reference to FIGS. 17 and 18. FIG. 18A shows a state in which the micropump is at a standstill. As shown in FIG. 18B, when the piezoelectric element 8 deforms upward, the inside of the pressure chamber 6 instantaneously becomes at a negative pressure, and hence a pressure difference arises between in front of and behind the valve mechanism 10A; the contacting part 11A of the valve mechanism 10A thus moves upward, whereby a gap is produced, and hence fluid flows into the pressure chamber 6. Upon the fluid flowing into the pressure chamber 6, the negative pressure is relieved, whereby the pressure difference between in front of and behind the valve mechanism 10A gradually disappears, and hence the load opening the contacting part 11A disappears. At this time, because the valve mechanism 10A is provided with an urging force (springiness) as shown in FIG. 17, upon the pressure difference dropping as described above, the contacting part 11A of the valve mechanism 10A is brought into contact with the central plate 3 by the urging force, whereby the flow path can be closed.
FIG. 18C shows a phenomenon in which the piezoelectric element 8 deforms downward and thus pushes the fluid out from the pressure chamber 6, showing a situation in which the pressure increases due to the piezoelectric element 8 pushing the fluid in the pressure chamber 6, and hence a pressure difference arises between in front of and behind the valve mechanism 10B of the first valve plate 2, and thus the valve mechanism 10B opens. Again, in this case, upon the fluid being discharged from the pressure chamber 6 to some extent, the pressure difference between in front of and behind the valve mechanism 10B disappears, and hence the contacting part 11B is brought into contact with the contacting part 11 due to the urging force possessed by the valve mechanism 10B, whereby the flow path can be closed. As the liquid delivery principle of the micropump, liquid is thus delivered by repeating movement from the state shown in FIG. 18A, through the state shown in FIG. 18B and the state shown in FIG. 18C, and back to the state shown in FIG. 18A, at a frequency of from several tens of Hz to several hundred Hz.
Each valve mechanism 10 thus separates away from the central plate 3 to create a flow path only when required, thus controlling the flowing in and out of the fluid. Moreover, in general, a function of the valve mechanism 10 being brought into contact with the central plate 3 through a certain urging force to close the flow path is required. As described above, as prior art for bestowing such an urging force, the technical method of an invention in which a spacer 15 is inserted between the valve mechanism 10 and the central plate 3, or the technical method of an invention in which a projecting part 16 is formed integrally is usual.
However, with the conventional constitution described above, in the case that a spacer 15 is installed, the various plates must be laminated and fixed together in a state in which the axial center of the spacer 15 and the axial center of each of the contacting part 11 of the valve mechanism 10 and the inflow hole 3a or the outflow hole 3b of the central plate 3 are aligned, and advanced assembly technology is required for this operation. Moreover, the size of a micropump used in medical equipment or a chemical analyzer is approximately a flat shape of dimensions 1 cm×1 cm with a thickness of 1.0 to 1.5 mm, and hence the volume allocated to the spacer 15 is only a diameter of 100 to 200 μm by a thickness of several tens of μm, and thus handling during the assembly process, and manufacture of the spacer 15 are not easy. Moreover, there are many factors impeding making the micropump thin, for example, despite being thin, the spacer 15 still has a thickness of several tens of μm, and hence space is required for accommodating the spacer 15, and moreover there is also the thickness of the adhesive layer in the case of fixing the spacer 15 to the central plate 3 (or the valve plate 2 or 4) using an adhesive.
In the case that a projecting part 16 is formed on the contacting part 11B of the valve mechanism 10B as shown in FIG. 16B, again as in the case of the spacer 15, the projecting part 16 is thin, and hence there is a problem that the assemblability including handling is poor. Furthermore, despite being thin, the thickness of the projecting part 16 cannot be ignored from the viewpoint of the micropump, and hence there are many factors impeding making the micropump thin.